A comparative analysis of the breeding biology of the lesser whitethroat and chiffchaff (Passeriformes, Sylviidae) in habitats with different degrees of urbanization (South Minusinsk basin)

This paper presents the results of long-term observations of nesting of two species of warblers inhabiting territories with different degrees of urbanization Sylvia curruca and Phylloscopus collybita. The research was carried out in the steppe and forest-steppe zone of the South Minusinsk basin. Both species are common and nest both in natural habitats and in the built-up part of the city. The lesser whitethroat arranges nests in the shrub layer only. The chiffchaff warbler has nests in a grassy tier in its natural habitats. The authors have revealed differences in the time of nesting in different altitudinal vegetation zones, as well as interspecific differences. The sizes of nests, clutches and eggs for different populations and in different years are determined. These parameters show variability, but no dependence on the environmental situation for them has been revealed. The survival rate of eggs and chicks and the overall efficiency of reproduction are evaluated. All the studied indicators of nesting biology, identified among the two species of warblers, are within the limits characteristic of the species. The differences revealed for populations located in natural and urbanized territories are manifested at the level of behavior of individuals (the nature of the nest location) and at the biocenotic level (the causes of the death of clutches). The authors have found no signs of isolation of urban populations.